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Hi Hendrik,
I have recently completed the adding of generics to the
databinding bundles. The way I approached this problem was to add
a new method that uses Collections and deprecated the method that
takes arrays. We use @SuppressWarning only on deprecated code, so
unless the users are using deprecated code we can be sure that we
are not breaking the types.
There is of course the issue of performance. In my opinion
cleaner code generally trumps questionable performance gains, but
that would be a case-by-case decision.
It is really good to see generics being added to JFace viewer.
JFace viewer was a large source of problems when adding generics
to databinding. I initially parameterized JFace collections with
<Object>. However that did not make it easy for the
consumers who would often have collections parameterized by
something else, but I was able to loosen the parameterization a
little by making all the immutable collections be parameterized by
a super class <? super E> to the element type in the
underlying collection <E>.
Another thing I ran against is that there are three methods that
return values with parameterization that is too loose. These are
Class.cast, Class.getComponentType, and Array.newInstance. If
you look in the e4 databinding repository at
org.eclipse.jface.databinding.util.Util, you will see the
following:
@SuppressWarnings("unchecked")
public static <E> Class<E> getComponentType(E[] a)
{
return (Class<E>) a.getClass().getComponentType();
}
@SuppressWarnings("unchecked")
public static <E> E[] createArrayInstance(Class<E>
componentType, int size) {
return (E[]) Array.newInstance(componentType, size);
}
So at least the warnings are isolated.
Let me know if there is anything I can do to help.
Nigel Westbury
On 26/07/2013 19:22, Lars Vogel wrote:
Based on an offline discussion with John, I
think @SuppressWarning is the better approach as this avoid the
unnecessary object creation.
Best regards, Lars
Am Freitag, 26. Juli 2013 schrieb Hendrik Still :
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Hi,
I'm currently adding generics support to the JFace Viewer. But
run
into problems with the generic typisation of mostly object
typed
arrays. I know arrays and generics do not mix very well. But
I'm not
able to replace arrays by lists, because this would break the
compatibility top older versions.
But how should I type/cast the arrays correctly?
Here is an example from the
org.eclipse.jface.viewers.LabelProviderChangedEvent Classe:
- ------------------------------------------------------------
private Object[] elements;
//...
public LabelProviderChangedEvent(IBaseLabelProvider
source, Object
element) {
super(source);
this.elements = new Object[1];
this.elements[0] = element;
}
- ------------------------------------------------------------
First solution would be this:
- ------------------------------------------------------------
private E[] elements;
//...
public
LabelProviderChangedEvent(IBaseLabelProvider<E> source,
E
element) {
super(source);
@SuppressWarnings("unchecked")
this.elements = (E[]) new Object[1]; //Warning
this.elements[0] = element;
}
- ------------------------------------------------------------
Second would be this:
- ------------------------------------------------------------
public LabelProviderChangedEvent(IBaseLabelProvider<E>
source, E
element) {
super(source);
ArrayList<E> arrayList = new
ArrayList<E>();
arrayList.add(element);
this.elements = (E[]) arrayList.toArray();
}
- ------------------------------------------------------------
What do you think is the better solution in the case of the
JFace
Toolkit? Or do you have a better idea to solve this problem?
Regars,
Hendrik
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